1. Field of the Invention
The present invention is directed to a process, system and apparatus for blocking ophthalmic lenses during edging and, in particular, to a system for blocking ophthalmic lenses that is particularly useful for lenses having slippery surface coatings.
2. Description of Related Art
In order to provide the proper shaped edge to an ophthalmic lens, so that the lens may properly fit into the frame of the eyeglasses, edging tools have long been used. These edging tools capture the ophthalmic lens between blocks applied to the lens surface and, using a frame guide having the configuration of the eyeglass frame, rotate the lens edge against a grinding wheel to impart the desired shape. One such edging tool is the Edgemaster sold by Oxford Corporation. In order to hold the block firmly to the surface of the ophthalmic lens, while at the same time permitting easy removal of the lens from the block without damage thereto, adhesive pads have been employed between the block and the lens surface. One such system is the LEAP System sold by the 3M Company comprising a high-density butyl rubber material having adhesives on both sides. More recent improvements to blocking tapes have been recorded in U.S. Pat. No. 6,149,750, wherein there is provided a tape having a polymeric backing and a pressure sensitive adhesive. The polymeric backing side is attached to the block and the adhesive side is attached to the lens surface.
A method of protecting the surface of the lenses during the edging process is disclosed in U.S. Pat. No. 5,451,281. This process utilizes a film having cling properties that is applied over the surface of the lens to protect it from scratching, except for the central portion of the lens. An opening is provided in the cling film to permit the blocking adhesive pad to adhere to the lens surface. Similar vinyl cling-type films have been used to protect lens surfaces during other processing, for example, during the drilling of holes in the lens for attachment to an eyeglass frame.
The development of certain types of coatings has resulted in difficulty in properly blocking lenses with the system described above. In particular, certain coatings such as super-hydrophobic anti-reflective (AR) coatings are very slippery and do not adhere well to pressure sensitive adhesives, so that the types of adhesives employed in the adhesive blocking pads described above are ineffectual in firmly holding the lens during edge grinding. As a result, there has been substantial slippage and general inability to properly secure the lens during edge grinding.